MTFCA Forum

To produce a period magneto battery charger consider this.

Dykes motor manual mentions a Warner battery charger for the Model T. The Warner system uses a wet RECTIFIER to convert AC from the Magneto to DC to charge the battery. The device would either be mounted on the outside running board, of if you had a coupe/roadster it could be inside the turtle back.

The electrolyte is a borax and water mixture. Popular Mechanics for 1924 and 1929 describe how to make such a RECTIFIER.

From an alternating current, such as the magneto, it is converted to D. C. with a light to control current/voltage. The jar’s two outer electrodes are aluminum, and the inner electrode is lead. The center becomes the negative DC voltage and the center tap from the transformer becomes the positive terminal for the DC voltage. (see from POPULAR MECHANICS, Oct. 1929, P655)
From 1909

From 1929

(I am not taking any responsibility for anyone attempting charging a battery with a magneto this way. This is presented to show others now long dead have looked for ways to charge a battery with a Model T Ford magneto .)

In my youth I made a number of transformers for custom applications. Mostly for converting old battery radios to run of 110. The A voltage (1.5 volts) for the filaments, the B voltage (90 volts) for the main power and in some cases the C voltage of I think about 9 volts. The A was ok as AC. The B of course had to be filtered DC. Also the C. The C drew very little current, so usually just ran it on dry cells.
The basics of making the transformers I got from a old popular Mechanics!!
I own a 1920 Detroit Electric and they ran on 84 volts and no transformers were needed to charge from 110 as the voltage drop in the rectifier was about 25 volts. But I suspect they were mostly vacuum tube version